Since the successful launches of Brentuximab vedotin (Adcetris) and Trastuzuinab emtansineo (Kadcyla), Antibody-drug conjugates (ADCs) have currently become a promising therapeutic modality for the clinical management of cancer. The new ADC compounds, which covalently incorporate the antitumor activity of a cytotoxic agent to a monoclonal antibody, have ability to deliver cytotoxic agents specifically to antigen-expressing tumor cells and then kill the tumor cells. The ADC platform includes a growing repertoire of cytotoxic agents, linker technologies, antibody properties, and conjugation methods. An important key factor in generating an optimal ADC is the cytotoxic agents.
Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a well-known class of sequence-selective DNA-binding agents derived from various Streptomyces species. Well-known members of this include DC-81, tomaymycin, porothramycin B, prothracarcin, mazethramycin, porothramycin, prothracarcin, sibanomycin, neothramycin, chicamycin, abbemycin, sibiromycin and anthramycin (I. O'Neil et al. Tetrahedron Letters 2003, 44, 7809-7812; L. Cipolla, et al, Anti-Cancer Agents in Medicinal Chemistry, 2009, 9, 1-31; L. Hurley, J. Antibiot. 1977, 30, 349; K. Schim/zu, et al. J. Antibiot 1982, 35, 992; J. Lown, et al. Biochem. Pharmacol. 1979, 28, 2017; D. Thurston, et al. Chem. Rev. 1994, 94, 433; P. Molina, et al. Tetrahedron 1995, 51, 5617; A. Kamal, et al. Chem. Commun. 1996, 385; A. Kamal, et al. Tetrahedron Lett. 1996, 37, 6803). These agents exert their antitumor antibiotics activity by the formation of a covalent adduct in the minor groove of a DNA with preference of a three base pairs of Pu-G-Pu (where Pu=purine; G=guanine) sequences, wherein their C11-position is electrophilic, enabling the molecules to alkylate the NH2 group of a guanine in the minor groove of DNA (Thurston, D. Molecular Aspects of Anticancer Drug-DNA Interactions; The Macmillan Press Ltd.: London, UK, 1993, pp 54-88, D. Antonow and D. Thurston, Chem. Rev. 2011, 111, 2815-2864; P. Dervan, Science 1989, 232, 464; L. Hurley, J. Med. Chem. 1989, 32, 2027; D. Thurston, Chem. Br. 1990, 26, 767). Moreover, PBDs have potential not only as antitumor agents but also as gene regulators and probes of DNA structure (Hurley, L. J. Med. Chem. (1989), 32: 2027-2033).
Thurston and co-workers reported the first C8/C8′-linked PBD dimer (DSB-120) in which two DC-81 subunits are joined through their aromatic A-ring at phenol positions by an inert propyldioxy linkage (D. Thurston, et al., J. Org. Chem. 1996, 61, 8141). These C8/C8′-diether-linked PBD dialers exhibit higher DNA binding affinity, at least twice compared to the monomer DC-81. The three carbon space ((n=3) C8/C8′-linked PBD dimer analog (DSB-120) covalently bind to a 5′-Pu-GATC-Py sequence by crosslinking opposite-strand guanines separately by 2 base pairs, span six DNA base pairs (Rahman, K. et al J. Am. Chem. Soc. (2009), 131(38), 13756-13766; Martin, C. et al Biochemistry (2005), 44(11), 4135-4147). The more extended PBD dimer (n=5) can span an extra base pair and cross-link the 5′-Pu-GA(T/A)TC-Py sequence (S. Hopton and A. Thompson, Biochemistry 2011, 50(21), 4720-4732, M. Smellie, et al, Biochemistry 2003, 42(27), 8232-8239; Gregson, S. et al J. Med. Chem. (2004), 47(5), 1161-1174). Among the C8/C8′-linked dimmers, the one with five carbon chain showed the highest cytotoxicities in most of the tested cell lines (Thurston, D. et al., J. Org. Chem. 1996, 61, 8141; Kamal, A. et al., Curr. Med. Chem.—Anti-cancer Agents, 2002, 2, 215-254, Gregson, S. et al J. Med. Chem. (2004), 47(5), 1161-1174). Since the introduction of C8/C8′-linked PBD dimer, a number of structurally modified PBD dimers have been synthesized and evaluated for their biological activity, particularly for their DNA binding ability and antitumor activity (see U.S. Pat. Nos. 8,383,618; 8,372,831; 8,217,167; 8,318,726; 8,153,627; 7,754,694; 7,741,319; 7,704,924; 7,612,062; 7,608,615; 7,557,099; 7,528,128; 7,528,126; 7,476,664; 7,465,724; 7,429,658; 7,407,951; 7,312,210; 7,265,105; 7,189,710; 7,183,054; 7,173,026; 7,067,511; 7,056,913; 7,049,311; 7,015,215; 6,979,684; 6,951,853; 6,939,869; 6,884,799; 6,800,622; 6,683,073; 6,660,856; 6,562,806; 6,362,331; Seifert, J. et al, Org. Biomol. Chem. (2012), 10(34), 6850-6860; Rahman, K et al J. Antimicro. Chem. (2012), 67(7), 1683-1696. Hartley, J. et al Cancer Research (2010), 70(17), 6849-6858; Hartley, J. et al Invest. New Drugs (2012), 30(3), 950-958; Howard, P. et al WO 2011130613; Hartley, J. et al Expert Opin. Invest. Drugs (2011), 20(6), 733-744; Howard, P. et al Bioorg. Med. Chem. Lett. (2009), 19(22), 6463-6466; Cipolla, L. et al Anti-Cancer Agents Med. Chem. (2009), 9(1), 1-31; Tiberghien, Ar. Bioorg. Med. Chem. Lett. (2008), 18(6), 2073-2077; Purnell, B. et al Bioorg. Med. Chem. Lett. (2006), 16(21), 5677-5681; Kamal, A. Bioorg. Med. Chem. (2006), 14(2), 385-394; Howard, P. et al WO 2005085259; Kumar, R. et al Eur. J. Med. Chem, (2005), 40(7), 641-654; Kamal, A. et al Bioorg. Med. Chem. (2004), 12(20), 5427-5436; Wilkinson, G. Invest. New Drugs (2004), 22(3), 231-240; Kumar, R. et al Mini-Reviews Med. Chem. (2003), 3(4), 323-339; Gregson, S. et al Bioorg. Med. Chem. Lett. (2001), 11(21), 2859-2862; Reddy, B. et al Anti-Cancer Drug Design (2000), 15(3), 225-238; Damayanthi, Y. et al J Org Chem 1999, 64, 290-292). Some structures of these dimers are shown in the Table 1. Interestingly, only the PBD dimers which have flexible linkers between two PBD subunits to form none distorting interstrand cross-links within the minor groove of DNA have been shown significantly increased the potency comparing to the PBD monomer. So far, a number of these compounds have been selected for preclinical studies but unfortunately most of them did not proceed beyond that stage mainly because of problems related to poor bioavailability. Therefore some of these PBD dimers have been conjugated to a cell binding agent, such as an antibody to enhance their bioavailability and therapeutic efficacy (see U.S. Pat. Nos. 8,426,402; 8,404,678; 8,163,736; 8,097,238; Commercon, A., et al. WO 2012014147; FR 2963007, Howard, P., et al WO 2011130598; Howard, P. et al WO 2011130613; Howard, P. et al WO 2011130616; Commercon, A. et al WO 2011023883; Bouchard, H. et al WO 2009016516 Gauzy, L. et al Eur. Pat. Appl. EP 2019104; Gauzy, L.; Zhao, Robert; et al WO 2007085930; Masterson, L. Bioorg, Med. Chem. Let. (2006), 16(2), 252-256; Li, W. et al WO 2012128868; Fishkin, N. et al WO 2012112687; Chari, R. WO 2012112708; Zhilina, Z. et al Bioconj. Chem. (2004), 15(6), 1182-1192; Kamal, A. et al Med Chem Comm (2011), 2(8), 780-8. Masterson, L. et al Bioorg. Med. Chem. Lett. (2006), 16(2), 252-6; Sagnou, M. et al Bioorg. Med. Chem. Lett. (2000), 10(18), 2083-2086; Rahman, K. M., et al. J Med Chem 2013, 56, 2911-35; Kamal, A. et al. Bioorg Med Chem Lett 2012, 22, 571-8; Hsieh, M. C, et al. Toxicol Appl Pharmacol 2011, 255, 150-9; Lee, C. et al, Chem Biol Interact 2009, 180, 360-7; Reddy, B. et at Anticancer Drug Des 2000, 15, 225-38). However, the PBD dimers, even some of them have been modified as a prodrug in antibody drug conjugates (WO 2012014147; WO 2012128868, WO 2012112687; WO 2011130616; Howard, P. et al Bioorg. Med. Chem. Lett. (2009), 19, 6463-6), are hardly soluble in a water based buffer solution, resulting in significant amount of antibody or protein aggregation. Here we disclose novel PBD dimer derivatives which have good antitumor antibiotic activities and especially they are linkable and can facilitate conjugation to a cell surface binding ligand in a water based medium without leading to protein aggregation. Thus they can be used effectively in a conjugate with a cell binding molecule for treating cancers and immune disorders.
TABLE 1Some of the published Pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimers   n = 3~6C8,C8′-linked PBD dimers (DSB-120, n = 3) SJG-136, a C8/C80-linked PBD dimers    n = 3~5, 8mixed imine- amide PBD dimers    R = H or CH3Tomaymycin dimers A PBD dimer (with C8/C8′ pyrrole-dicar- boxylic acid amide linkers)    n = 3~6C8/C80-linked PBD dimers Indolinobenzo- diazepine dimers mixed imine- amine Indolino- benzodiazepine dimers Sulfate prodrug of a PBD dimer C8/C-C2 amide-linked PBD dimer C2/C2′-linked PBD dimers